This section provides background information related to the present disclosure which is not necessarily prior art.
In a multi-speed epicyclic transmission, various elements within the transmission are alternately held from rotation relative to a housing or are coupled to another element of the transmission to cause the components to co-rotate to cause the transmission to operate in the several different overall gear ratios. When one or more elements of an epicyclic transmission are coupled together to co-rotate, the coupling that is used to couple the elements together needs to rotate with the rotating elements of the transmission. If a multi-plate friction clutch were to be used to couple the elements together, it would be necessary to apply a normal force to the rotating friction clutch.
One way to apply a normal force to the rotating friction clutch is to have a stationary element that is capable of exerting a force on the friction clutch act through a thrust bearing. This solution, however, suffers from the drawback that the bearing imparts a relatively high drag force that reduces the efficiency of the transmission.
Another way to apply a normal force to the rotating friction clutch is to use a piston assembly that rotates with the friction clutch and to distribute fluid power to the piston assembly through a rotary seal. This solution, however, suffers from the drawback that the rotating seal creates drag and necessitates a continuous supply of pressurized fluid to maintain a desired pressure due to leakage.
Accordingly, there remains a need in the art for an improved multi-speed epicyclic transmission.